My concern is whether the PLF will absorb just enough thermal and aerodynamic load as the vehicle descends that IRNSS-1H might be released into the middle or lower atmosphere at a low enough speed to survive the descent to the surface largely intact.

Logged

"Oops! I left the silly thing in reverse!" - Duck Dodgers

~*~*~*~

The Space Shuttle Program - 1981-2011

The time for words has passed; The time has come to put up or shut up!DON'T PROPAGANDISE, FLY!!!

The PSLV-C39 rocket, which failed to launch the IRNSS 1H satellite on Thursday, was dragged down by at least one tonne of extra weight from the unseparated heat shield after the second stage, its velocity reduced by one kilometre per second. This greatly reduced the altitude it was to reach for a successful mission, say scientists privy to the project.

So the mission failed because the rocket failed to reach proper orbit, hmm so interesting.

Silly me I thought it failed because the payload was trapped inside the fairing.

The Failure Analysis Committee, headed by VSSC Director K.Sivan, is poring through the flight data of the mission in a bid to understand what went wrong. Dr.Sivan toldThe Hindu that a simulation exercise would be carried out to zero in on the exact reason. We are on track and hope to reach a conclusion within a week, he said.

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Based on the initial inference, informed sources at ISRO said the command for separation had gone through but failed to trigger the mechanical process that pops open the heat shield. They said the investigations were likely to centre on the electrically-initiated pyro devices that initiate the sequence of separation.

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What is intriguing for scientists is that the pyro device which probably malfunctioned, is based on an electro-mechanical process, one that is far less complex than thousands of other components in the rocket.

Isro chairman AS Kiran Kumar on Saturday firmly denied that the PSLV-C39 rocket carrying eighth navigation satellite IRNSS-1H failed on Thursday as it was carrying one-tonne extra load. A report in TOI on Saturday had stated that "the PSLVC39 rocket, which failed to launch the IRNSS-IH, was dragged down by at least onetonne extra weight". The report stated that this was more than the design permitted.

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Speaking to TOI on Saturday prior to making a presentation at the Nehru Centre in Mumbai, the Isro chief said: "The report is incorrect and the rocket was not carrying any extra load." He said the heat shield added additional weight to the launch vehicle as it failed to get detached at the second stage and went along till the fourth stage separation point. "It was not because Isro put any additional weight prior to the launch," he said.

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He added that a portion of the rocket with the satellite enclosed in the heat shield was currently orbiting 163km x 6,600 km and was being tracked by the multi-object tracking radar at Satish Dhawan Space Centre, Sriharikota. "It is expected to remain this way for another 25 days,'' he said. Kiran Kumar said a failure analysis committee was being formed to study the setback.

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Dr K Sivan, director of Thiruvananthapuram-based Vikram Sarabhai Space Centre (VSSC), said, "Launch failure will not affect future missions as they will go as planned. But corrective measures will be taken in future for all types of vehicles as the heat shield separation mechanism is similar in all launchers."

The primary function of heat shield is to protect the payload and other sensitive system of launch vehicle from the aerodynamic and thermal loads during its ascent phase of flight and to provide the aerodynamic shape and thereby reduces the aerodynamic drag. After meeting the functional requirements the heat shield should be separated from the launch vehicle as early as possible. The system used for separation should impart necessary jettisoning velocity to achieve collision free separation. The heat shield is usually made in two halves and attached through separation system. The velocity required for safe separation depends on the heat shield diameter, mass, flexibility and the state of motion. However as the diameter and length of the heat shield goes up flexibility plays a major role in safe separation. Also for many vehicles the heat shield separation takes place in thrusting phase. All these factors necessitate a larges separation velocity and jettisoning system to impart this velocity as quickly as possible. For these reasons the PSLV and GSLV have adopted a zip cord as jettisoning system for vertical separation. The separation dynamics of heat shield is studies by combining the rigid body as well as flexible motions of the fairings using finite element method. Fig [5]  HEAT SHIELD SEPARATION

The use of the term "heat shield" for the component that failed on this launch is incorrect and confusing. A heat shield protects spacecraft during reentry, a payload shroud protects them during launch. They are physically very different.

The use of the term "heat shield" for the component that failed on this launch is incorrect and confusing. A heat shield protects spacecraft during reentry, a payload shroud protects them during launch. They are physically very different.

Related question: What will they call the heat shield when they start flying crewed capsules or other spacecraft?

The use of the term "heat shield" for the component that failed on this launch is incorrect and confusing. A heat shield protects spacecraft during reentry, a payload shroud protects them during launch. They are physically very different.

That's the modern US usage. However, it wasn't always that way. The 1960s NASA Scout launch vehicle's nosefairing was always referred to as its heat shield. And it's clearly not incorrect, in that it does shield the payloadfrom the heat (ok, and ram pressure) of ascent.

I have the impression that Langley used 'heat shield', Marshall used 'nose cone', and the west coast used 'payload fairing', but it may not have been that systematic. In the US, terminology eventually standardized on 'payload fairing' for the forward heat shield and 'heat shield' for the reentry heat shield. But that's US English. Indian English is perfectlyfree to standardize on a different usage, and has done.

The stage 4 was always intended to burn to exhaustion. However, given that they cannot have had communications with IRNSS-1H whilst it was still in the PLF, I am sceptical that they were able to vent its prop tanks. We probably have either a mistranslation or someone lower down the chain in IRSO telling their top echelon what they want to hear.